<!DOCTYPE html>
<html lang="en">
<head>
	<meta charset="UTF-8">
	<title>包装类</title>
</head>
<body>
	<script>
		var str = 'abc';
		str += 1;
		var test = typeof(str); //test == 'string'
		if (test.length == 6) {
			tset.sign = 'typeof的返回结果可能是String'
		}
		console.log(test.sign);
	</script>
</body>
</html>